This invention generally relates to a process for the recovery of vegetable protein material and more specifically to the formation of a vegetable protein concentrate from defatted soybean material.
This invention was conceived and developed largely for soy materials because of the special problems encountered with such materials. Therefore, it will be explained largely with respect to soy materials, and has special application to such materials, although it can be used for other oilseed protein materials in the broader aspects of the invention.
Protein concentrates derived from vegetable protein material such as soybeans enjoy widespread commercial use to fortify foods and beverages in order to increase their nutritional value. The term "concentrate" is defined in the art as a vegetable protein material having a protein concentration of between 70 and 90% by weight, and is usually obtained by the partial removal of non-proteinaceous material from defatted vegetable protein material in order to increase the resultant protein concentration to greater than 70% by weight. Many processes are known for soybean concentration production including washing techniques wherein defatted soybean flakes are washed with solvents such as water, aqueous alcohol, or dilute acids to remove soluble carbohydrates and increase the protein content to 70% or higher. For example, U.S. Pat. No. 3,734,901 describes a two-stage extraction to remove lipids and water soluble constituents from soybean flakes to obtain a concentrate. However, the soybean concentrate of the present invention is extracted and separated from carbohydrate material in a facile method that permits the soy protein to retain excellent functional properties while lacking the common, bitter, beany taste and objectionable odor and color of concentrates made from conventional processes.
Generally speaking, some techniques for producing protein isolates are applicable in the production of protein concentrates from oilseed materials. A protein isolate can be generally characterized as a product resulting from the extraction, subsequent concentration and purification of proteinaceous material from a proteinaceous source such as vegetable protein or oilseed material. Typically, the protein isolate on a moisture free basis will have a protein content which will range between about 90 and 98% by weight after isolation of the protein and separation from the non-proteinaceous and cellular material present in most types of vegetable protein material. Isolates are generally produced by dissolving a vegetable protein material in the form of an oilseed meal such as soybean meal above or below the isoelectric point of the soy protein and then adjusting the pH of the solution to the isoelectric point to precipitate the purified protein. At this point in the process, the protein curd or precipitated, purified protein has adequate functional properties. However, in many food applications, it is not considered to possess the best flavor since undesirable flavor components remain entrapped in the precipitated protein and further processing is normally required to provide an isolate with a bland flavor to be suitable for use in a variety of food products. Therefore, additional centrifugation or separation of the protein is carried out in order to remove any entrapped undesirable flavor components. Repeated washing of the precipitated curd is needed to remove most of the entrapped flavor components. However, it has been recognized that while washings of the curd with either water, alcohols or mixtures thereof results in an improvement in flavor; nevertheless, repeated processing of this type reduces the overall efficiency of the isolation process since a certain percentage of the protein is lost during each washing step thereby reducing the yield. The more processing that is involved the more likely one is to destroy the desirable functional properties of the proteinaceous components and the less flexibility there is in regard to the quality of proteinaceous material from which the concentrate or isolate is prepared.
Recently, new techniques in protein isolation have described means for isolating intact protein bodies directly from the vegetable protein source material, without solubilization of the proteinaceous material or preliminary washings for carbohydrates. Theoretically, the removal of the intact protein bodies to form a concentrate or isolate would avoid undesirable interactions of the proteins and other cellular components of the protein material which diminish functional properties of the protein material or have other undesirable side effects. A technique of the above type for the recovery of the intact protein bodies from a vegetable source material without solubilization is that of density gradient centrifugation or fractionation. This technique involves the use of a medium having a specific density range with the ground proteinaceous material containing intact protein bodies, starch, fat and other cellular material that is dispersed followed by centrifugation thereof. Centrifugation provides a separation of the intact protein bodies, the cellular material and fat in three different phases. Removal of a phase containing protein bodies obviously provides protein material whose protein content has been increased. Techniques involving the isolation of intact protein bodies using density fractionation are described in U.S. Pat. Nos. 3,828,017 and 3,869,438 wherein the mixture of a fluorocarbon and a low density hydrocarbon are employed as the medium having a density of 1.35 to 1.45 for fractionation of the ground protein material from oilseeds. Other mediums used in the fractionation of intact soybean protein bodies include aqueous sucrose solutions having a density of 1.28 to 1.32 as described in Plant Physiology 42 page 797 (1967), and mixtures of oil and carbontetrachloride and having a density between 1.36 and 1.39 as described in Journal of Agriculture and Biological Chemistry 30 page 1133 (1966).
Methods concerning the production of oilseed concentrates are shown in U.S. Pat. No. 2,881,076 wherein the native protein is insolubilized in an aqueous solution with a pH of 4.0 to 4.8; Canadian Pat. No. 697,264 shows the use of an aqueous extracting agent and high temperatures to remove the bitter or beany flavor from defatted soy meal to produce a concentrate and U.S. Pat. No. 3,895,003 describes a process for producing oilseed protein concentrates by particle size classification. This disclosure teaches a two step grinding procedure followed by a water or alcohol washing to produce a soy concentrate product. The differential grinding of the soy material is permitted because of the inherent large particle size of the cellular materials which makes them susceptible to easy reduction in size. Additionally, it is relatively difficult to reduce the size of the protein bodies by grinding. Thus, protein separation and concentration is accomplished by grinding, air classifying and washing of the coarse particle fraction of the soy material with alcohol or water at a pH of 4 to 6 and separating the insoluble protein from the washed solution.
U.S. Pat. No. 3,901,725 describes a wet process for separating wheat starch granules according to size. The particular large size of the granules permits a large variety of uses. U.S. Pat. No. 3,972,861 relates to the preparation of cottonseed protein concentrate by grinding and liquid cyclone separation. The separation of the protein in the cottonseed takes place with relative ease due to the large size of the pigment glands and cellular fraction.
The present invention represents an improvement in the art for the separation of protein concentrates, especially those derived from soy protein. The preferred yield of protein bodies from a vegetable protein material is obtained from the present process which describes critical parameters necessary to provide protein concentrates which have not undergone extensive washing with either alcohol or water, but yet still retain improved flavor and functional characteristics.